An echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is essentially a sonogram of the heart. Also known as a cardiac ultrasound, echocardiography uses standard ultrasound techniques to image two-dimensional slices of the heart.
Stress echocardiography is a test that uses ultrasound imaging to determine how the heart muscles respond to stress or increased performance load. The purpose of the procedure is to discover and treat any potential or actual blockage or disease before serious or life-threatening problems develop. Stress echocardiography is different from an exercise stress test in the way that ultrasound images are taken and used for the diagnosis. The test is performed to see whether the heart muscle is getting enough blood flow and, therefore, sufficient oxygen when it is working hard, i.e., under stress. The test will usually be ordered when patients:                have new symptoms of angina or chest pain;        have angina that is becoming worse;        have recently had a heart attack;        are at high risk for heart disease (before having surgery or when beginning an exercise program); and        have heart valve problems.        
Typically, stress echocardiography includes the following steps:                the echocardiogram is performed while the patient is rested and inactive;        the patient is asked to exercise, such as going on a treadmill or given medicine until the target heart rate is achieved in order to reveal how the heart works when the patient is active;        the blood pressure and heart rhythm (ECG) of the patent is throughout the procedure;        the ultrasound images are monitored and recorded during the procedure;        performing a second echocardiogram immediately after the target heart rate has been reached; and        analyzing ultrasound imaging which will reveal any parts of the heart that may not be receiving enough blood or oxygen because of blocked arteries.        
As mentioned earlier, during stress echocardiography the patients are requested to perform exercises such as walking on a treadmill or pedaling on an exercise bike. However, for patients who are not fit enough to perform these types of tasks, they will be receiving a medication such as Dobutamine or other IV drugs to increase their heart rate to the target heart rate before taking the second echocardiogram.
It would be advantageous to avoid the use of any IV drugs on patients who are unable to perform the exercises for a stress echocardiography test. It would be advantageous to provide a surrogate test that could be given to patients for stress echocardiography.